The present invention is directed to novel methods and apparatus for producing and treating elastomer composites, and to novel elastomer composites produced using such methods and apparatus. More particularly, the invention is directed to continuous flow methods and apparatus for producing and treating elastomer masterbatch of particulate filler finely dispersed in elastomer, for example, elastomer composites of carbon black particulate filler finely dispersed in natural rubber, and rubber materials and products formed of such masterbatch compositions.
Numerous products of commercial significance are formed of elastomeric compositions wherein particulate filler is dispersed in any of various synthetic elastomers, natural rubber or elastomer blends. Carbon black, for example, is widely used as a reinforcing agent in natural rubber and other elastomers. It is common to produce a masterbatch, that is, elastomer coagulated with carbon black or other filler and optionally containing various additives, such as extender oil. Carbon black masterbatch can be prepared with different grades of carbon black, that is, carbon blacks which vary both in surface area per unit weight and in xe2x80x9cstructure.xe2x80x9d
While a wide range of performance characteristics can be achieved employing currently available materials and manufacturing techniques, there has been a longstanding need in the industry to develop elastomeric compositions having improved properties and to reduce the cost and complexity of current manufacturing techniques. In particular, it is known for example that macro-dispersion level, that is, the uniformity of dispersion of the carbon black or other filler within the elastomer, can significantly impact performance characteristics. For elastomeric compositions prepared by intensively mixing the carbon black or other filler with natural rubber or other elastomer (such as in a Banbury mixer or the like), any increase in macro-dispersion requires longer or more intensive mixing, with the consequent disadvantages of increased energy costs, manufacturing time, and similar concerns. For carbon black fillers of certain surface area and structure characteristics, dispersion beyond a certain degree has not been possible or commercially practicable using known mixing apparatus and techniques. In addition, such prolonged or more intensive mixing degrades the natural rubber or other elastomer by reducing its molecular weight, rendering the finished elastomeric compound undesirable for certain applications.
In addition to dry mixing techniques, it is known to continuously feed latex and a carbon black slurry to an agitated coagulation tank. Such xe2x80x9cwetxe2x80x9d techniques are used commonly with synthetic elastomer, such as styrene-butadiene rubber (SBR). The coagulation tank contains a coagulant such as salt solution or an aqueous acid solution typically having a pH of about 2.5 to 4. The latex and carbon black slurry are mixed and then coagulated in the coagulation tank into small beads (typically a few millimeters in diameter) referred to as wet crumb. The crumb and acid (or saline) effluent are separated, typically by means of a vibrating shaker screen or the like. The crumb is then dumped into a second agitated tank where it is washed to achieve a neutral or near neutral pH. Thereafter the crumb is subjected to additional vibrating screen and drying steps and the like. Variations on this method have been suggested for the coagulation of natural and synthetic elastomers. In U.S. Pat. No. 4,029,633 to Hagopian et al, which like the present invention is assigned to Cabot Corporation, a continuous process for the preparation of elastomer masterbatch is described. An aqueous slurry of carbon black is prepared and mixed with a natural or synthetic elastomer latex. This mixture undergoes a so-called creaming operation, optionally using any of various known creaming agents. Following the creaming of the carbon black/latex mixture, it is subjected to a coagulation step. Specifically, the creamed carbon black/latex mixture is introduced as a single coherent stream into the core of a stream of coagulating liquor. The solid stream of creamed carbon black/latex mixture is said to undergo shearing and atomizing by the stream of coagulating liquor prior to coagulation, being then passed to a suitable reaction zone for completion of the coagulation. Following such coagulation step, the remainder of the process is substantially conventional, involving separation of the crumb from the waste product xe2x80x9cserumxe2x80x9d and washing and drying of the crumb. A somewhat similar process is described in U.S. Pat. No. 3,048,559 to Heller et al. An aqueous slurry of carbon black is continuously blended with a stream of natural or synthetic elastomer latex. The two streams are mixed under conditions described as involving violent hydraulic turbulence and impact. As in the case of the Hagopian et al. patent mentioned above, the combined stream of carbon black slurry and elastomer latex is subsequently coagulated by the addition of an acid or salt coagulant solution.
Since good dispersion of a coagulating filler in the elastomer has been recognized for some time as being important for achieving good quality and consistent product performance, considerable effort has been devoted to the development of procedures for assessing dispersion quality in rubber. Methods developed include, e.g. the Cabot Dispersion Chart and various image analysis procedures. Dispersion quality can be defined as the state of mixing achieved. An ideal dispersion of carbon black is the state in which the carbon black agglomerates (or pellets) are broken down into aggregates (accomplished by dispersive mixing) uniformly separated from each other in the elastomer (accomplished by distributive mixing), with the surfaces of all the carbon black aggregates completely wetted by the rubber matrix (usually referred to as incorporation).
Macro-dispersion of carbon black or other filler in uncured natural rubber or other suitable elastomer can be assessed using image analysis of cut surface samples. Typically, five to ten arbitrarily selected optical images are taken of the cut surface for image analysis. Knife marks and the like preferably are removed using a numerical filtering technique. Cut surface image analysis thus provides information regarding the carbon black dispersion quality inside a natural rubber compound. Specifically, percent undispersed area D(%) indicates carbon black macro-dispersion quality. As macro-dispersion quality is degraded, percent undispersed area increases. Dispersion quality can be improved, therefore, by reducing the percent undispersed area.
A commercial image analyzer such as the IBAS Compact model image analyzer available from Kontron Electronik GmbH (Munich, Germany) can be used to measure macro-dispersion of carbon black or other filler. Typically, in quantitative macro-dispersion tests used in the rubber industry, the critical cut-off size is 10 microns. Defects larger than about 10 microns in size typically consist of undispersed carbon black or other filler, as well as any grit or other contaminants, which can affect both visual and functional performance. Thus, measuring macro-dispersion involves measuring defects on a surface (generated by microtoming, extrusion or cutting) greater than 10 microns in size, by total area of such defects per unit area examined, using an image analysis procedure. Macro-dispersion D(%) is calculated as follows:       Undispersed    ⁢          xe2x80x83        ⁢    area    ⁢          xe2x80x83        ⁢          (      %      )        =            1              A        m              ⁢                  ∑                  i          =          1                m            ⁢              xe2x80x83            ⁢                        N          i                ⁢                  xe2x80x83                ⁢                              π            ⁢                          xe2x80x83                        ⁢                          D              i              2                                4                    
where
Am=Total sample surface area examined
Ni=Number of defects with size Di 
Di=Diameter of circle having the same area as that of the defect (equivalent circle diameter)
m=number of images
There has long been a need in various industries for elastomeric compounds of particulate filler dispersed in suitable elastomer, especially, for example, carbon black dispersed in natural rubber, having improved macro-dispersion. As discussed above, improved macro-dispersion can provide correspondingly improved aesthetic and functional characteristics. Especially desirable are new elastomeric compounds of carbon black in natural rubber wherein improved macro-dispersion is achieved together with controlled Mooney Viscosity, higher molecular weight of the natural rubber, and higher amount of bound rubber.
It is an object of the present invention to meet some or all of these long felt needs.
In accordance with a first aspect, a method of treating a substantially coagulated masterbatch having a particulate filler and an elastomer includes the steps of feeding the masterbatch to a feed port of a continuous compounder having multiple rotors axially oriented in an elongate processing chamber; processing the masterbatch through the processing chamber of the continuous compounder by controlled operation of the rotors; and discharging the masterbatch from a discharge orifice of the continuous compounder.
In certain preferred embodiments, the method may also include the step of passing the masterbatch from the discharge orifice of the continuous compounder through an open mill and/or the step of compounding additional material into the masterbatch in the continuous compounder. In certain preferred embodiments, the additional material may be selected from additional filler, additional elastomer, a second masterbatch, oil and other additives. In certain preferred embodiments, the continuous compounder dries the masterbatch. In certain preferred embodiments, the continuous compounder controls the Mooney Viscosity of the masterbatch.
In accordance with another aspect, a continuous flow method of producing elastomer composite includes the steps of feeding a continuous flow of first fluid including elastomer latex to a mixing zone of a coagulum reactor defining an elongate coagulum zone extending from the mixing zone to a discharge end; feeding a continuous flow of second fluid having particulate filler under pressure to the mixing zone of the coagulum reactor to form a mixture with the elastomer latex, the mixture passing as a continuous flow to the discharge end and the particulate filler being effective to coagulate the elastomer latex, wherein mixing of the first fluid and the second fluid within the mixing zone is sufficiently energetic to substantially completely coagulate the elastomer latex with the particulate filler prior to the discharge end; discharging a substantially continuous flow of elastomer composite from the discharge end of the coagulum reactor; feeding the substantially continuous flow of elastomer composite to a feed port of a continuous compounder having multiple parallel rotors axially oriented in an elongate processing chamber; processing the elastomer composite through the processing chamber of the continuous compounder by controlled operation of the rotors; and discharging the elastomer composite from a discharge orifice of the continuous compounder. In certain preferred embodiments, the method also includes the step of processing the elastomer composite from the discharge orifice of the continuous compounder through an open mill.
In accordance with another aspect, an apparatus for producing elastomer composite of particulate filler dispersed in elastomer has a coagulum reactor defining a mixing zone and an elongate coagulum zone extending from the mixing zone to a discharge end; latex feed means for feeding elastomer latex fluid continuously to the mixing zone; filler feed means for feeding particulate filler fluid as a continuous jet into the mixing zone to form a mixture with the elastomer latex fluid traveling from the mixing zone to the discharge end of the coagulum zone, wherein the distance between the mixing zone and the discharge end is sufficient to permit substantially complete coagulation of the elastomer latex prior to the discharge end; and a continuous compounder having a feed port operatively connected to the discharge end of the coagulum zone for receiving the coagulated mixture of elastomer latex and particulate filler, a discharge orifice, an elongate processing chamber, and a plurality of rotors axially oriented within the processing chamber. In certain preferred embodiments, the apparatus further has conveying means for conveying a substantially continuous flow of elastomer composite from the discharge end of the coagulum zone to the feed port of the continuous compounder.
In accordance with another aspect, an elastomer composite has substantially coagulated elastomer in which particulate filler has been dispersed by feeding a continuous flow of first fluid having elastomer latex to a mixing zone of a coagulum reactor defining an elongate coagulum zone extending from the mixing zone to a discharge end; feeding a continuous flow of second fluid having particulate filler under pressure to the mixing zone of the coagulum reactor to form a mixture with the elastomer latex, the mixture passing as a continuous flow to the discharge end, and the particulate filler being effective to coagulate the elastomer latex, wherein mixing of the first fluid and the second fluid within the mixing zone is sufficiently energetic to substantially completely coagulate the elastomer latex with the particulate filler prior to the discharge end; discharging a substantially continuous flow of elastomer composite from the discharge end of the coagulum reactor; feeding the elastomer composite from the discharge end of the coagulum reactor to a continuous compounder having multiple parallel elongate rotors axially oriented in an elongate processing chamber; processing the masterbatch through the processing chamber of the continuous compounder by controlled operation of the rotors; and discharging the masterbatch from a discharge orifice of the continuous compounder.
In accordance with another aspect, masterbatch is processed in a continuous compounder as described above along with the addition of other materials. Specifically, the additional materials may be additional filler; additional elastomers; additional masterbatch, comprising elastomer composite and carbon black or other filler; any of various known additives used in elastomer composites, such as antioxidants, antiozonants, plasticizers, processing aids (e.g., liquid polymers, oils and the like), resins, flame-retardants, extender oils, lubricants, and a mixture of any of them; and a vulcanization system, or a mixture of any of these.
In accordance with another aspect, a method for preparing elastomer masterbatch comprises feeding simultaneously a particulate filler fluid and an elastomer latex fluid to a mixing zone of a coagulum reactor, followed by further processing in a de-watering extruder and continuous compounder, as disclosed above. Most preferably the coagulum reactor , de-watering extruder and the continuous compounder operate together in a continuous flow production line. A coagulum zone of the coagulum reactor extends from the mixing zone, preferably progressively increasing in cross-sectional area in the downstream direction from an entry end to a discharge end. The elastomer latex may be either natural or synthetic and the particulate filler fluid comprises carbon black or other particulate filler effective to coagulate the latex. The particulate filler fluid is fed to the mixing zone preferably as a continuous, high velocity jet of injected fluid, while the latex fluid is fed at low velocity. The velocity, flow rate and particulate concentration of the particulate filler fluid are sufficient to cause high shear mixing with the latex fluid and flow turbulence of the mixture within at least an upstream portion of the coagulum zone, so as to substantially completely coagulate the elastomer latex with the particulate filler prior to the discharge end. Substantially complete coagulation is thus achieved, in accordance with preferred embodiments, without the need of employing an acid or salt coagulation agent. The coagulum reactor is discussed in detail in commonly owned and copending U.S. application Ser. No. 08/823,411 and in Published PCT application Ser. No. PCT/US97/05276, both of which are incorporated herein by reference. The masterbatch from the coagulum reactor is fed through a de-watering extruder to remove the bulk of the water from the masterbatch and then into a feed port of the continuous compounder disclosed above, preferably in a continuous flow stream from the coagulum reactor. The continuous compounder dries the elastomer masterbatch, provides control over the Mooney Viscosity of the elastomer masterbatch and, in certain preferred embodiments, control over other characteristics and performance properties of the masterbatch via manipulation of continuous compounder operating parameters, including rotor speed, throughput rate, discharge orifice opening size, discharge orifice temperature and processing chamber temperature. The masterbatch may, in accordance with certain preferred embodiments, optionally be further processed after the continuous compounder by an open mill to further control the Mooney Viscosity of the masterbatch. This is especially advantageous, since the elastomer masterbatch produced by the coagulum reactor may have a Mooney Viscosity which is too high for use in certain applications. Further processing of the masterbatch by the continuous compounder and the open mill is now found to provide excellent product control to achieve a desired Mooney Viscosity and moisture level.
In especially preferred embodiments, the above disclosed de-watering extruder is connected to the coagulum reactor by a conveyor or conduit for carrying masterbatch from the coagulum reactor to the de-watering extruder, and the continuous compounder is directly downstream of the de-watering extruder, such that the masterbatch is produced and treated in a continuous flow process. Thus, a continuous process line is created for the formation and treatment of elastomer masterbatch, which provides for significantly enhanced economies of production. Use of the continuous compounder with a de-watering extruder and coagulum reactor in a continuous process line can facilitate controlling and changing operating parameters of the masterbatch production and treatment line without interrupting the continuous process line.
In accordance with an apparatus aspect, a coagulum reactor, de-watering extruder and continuous compounder described above are coupled in a masterbatch production and treatment line. In accordance with certain preferred embodiments, an open mill is provided to cool the elastomer masterbatch and further control its Mooney Viscosity after it passes through the continuous compounder.
In accordance with another apparatus aspect, means are provided for feeding elastomer latex fluid to the mixing zone of the aforesaid coagulum reactor, preferably under low pressure, substantially laminar type flow conditions, and means are provided for simultaneously feeding particulate filler fluid to the mixing zone under pressure sufficient to create a jet of adequate velocity or kinetic energy to entrain the elastomer latex, as described above, and achieve coagulation before the product flowing downstream from the mixing zone reaches the discharge end of the coagulum reactor. In accordance with certain preferred embodiments described in detail below, means for feeding the elastomer latex fluid and separate means for feeding the particulate filler fluid each may comprise a feed channel in a mixing head integral with a substantially tubular member defining the coagulum zone. The mixing zone may be provided at the junction of such feed channels within the mixing head. In accordance with certain preferred embodiments, the mixing zone is simply a coaxial extension of the coagulum zone. Progressive increase in the cross-sectional area of the coagulum reactor is continuous in certain preferred embodiments and is step-wise in other preferred embodiments. A de-watering extruder and continuous compounder are positioned downstream of the coagulum reactor to further process the elastomer masterbatch, providing drying and control of the Mooney Viscosity and other physical properties and performance characteristics of the elastomer masterbatch. In certain preferred embodiments, an open mill may be coupled to the discharge orifice of the continuous compounder, either directly or via a conveyor or other conduit, to provide yet further treatment of the elastomer masterbatch. Additional optional and preferred features of the apparatus disclosed here for continuous flow production of elastomer masterbatch are discussed in the detailed description below.
In accordance with yet another aspect, elastomer composites are provided as a product of the process or apparatus disclosed above. In accordance with preferred embodiments, novel elastomer composites are provided having macro-dispersion level of the particulate filler, molecular weight of the elastomer, particulate loading level, choice of particulate filler (including, for example, carbon black fillers of exceptionally high surface area and low structure), controlled Mooney Viscosity and/or other physical properties or performance characteristics not previously achieved. Additionally, a suitable balance can be obtained between the molecular weight and bound rubber of the masterbatch for a given Mooney Viscosity. In that regard, the methods and apparatus disclosed here can achieve excellent macro-dispersion, even of certain fillers, such as carbon blacks having a structure to surface area ratio DBP:CTAB less than 1.2 and even less than 1, in elastomers such as natural rubber, while minimizing degradation of the molecular weight of the elastomer and highly controlled Mooney Viscosity. In accordance with yet other aspects of the invention, intermediate products are provided as well as final products which are formed of the elastomer composites produced by the method or apparatus disclosed here, e.g., tires and tire components. Further examples of such final products are listed below.
These and other aspects and advantages of various embodiments of the invention will be further understood in view of the following detailed discussion of certain preferred embodiments.